Measuring low impedance using the S21 shunt method

I know the ENA has a feature that allows impedance measurements with two port S21 approach. From what I have read it appears that the lowest practical impedance measurement floor would be about 0.5 Ohm with that approach.

I'm working with a mutual customer who would like to be able to measure down to 10 milliOhm @ 150MHz, 20 milliOhm @ 500MHz, 50 milliOhm @ 1GHz, and 500 milliOhm @ 10GHz. But so far I think he is out of luck since it appears no instruments measure such low impedance at such frequencies. But maybe I'm overlooking something. Let me know what advice you can give me.

Take a look at the app note listed below. It discusses a solution from Ultimetrix, Inc. called the Power Delivery Network Analyzer (PDNA) that uses a PNA family network analyzer, test set, and add on software to implement this test technique for low impedance measurements.

OJ,Thanks. But that apnote can most politely be described as a sales pitch for an unproven product that has no traceable accuracy and completely lacks any guaranteed performance specifications. Tell me I'm wrong. And as a forum moderator you should feel free to delete this reply if you feel it damages Agilent or Ultimetrix.

In response to the last post by Craig K. regarding making ultra low impedance measurements using the S21 shunt method, in actuality, the appl. note that OJ references provides all of the information that you need to make the measurements that you described. I have incorporated this very same "not so well known" measurement technique in the (on-wafer) characterization and modeling of MIM Capacitors, and am able to reliably extract resistances on the order of 30m-Ohm < Rs < 100m-Ohm on test structures of varying geometry. The fact of the matter is that making these measurements does not require the use of the P4200 at all, as I routinely use a PNA as well as an HP-8753ES to acquire the necessary data. If de-embedding of your (shunt configured) DUT is required, you must first do so to the electrical center of the device / test structure. Once you have de-embedded the DUT, simply compute the shunt network impedance per pg. 13 of the app. note as Zp = 25 * [S21 / (1-S21)]. The resistance that you are looking for can be found from real(Zp). Any series reactive component that exists can be found in terms of imag(Zp). If you have the S-Parameters of the test setup, you can also determine the resistive impedance graphically as the Y-interecpt of real(Zp) vs omega^2, which can also be done programmatically via use of the linfit or autofit functions in ICCAP.